MapReduceIndexer keeps better track of lastSequenceIndexed

Allows caller to specify the value, in case it's greater than any
sequence that was passed to the indexer (i.e. a doc was skipped.)

For couchbase/couchbase-lite-ios#1379

C/c4View.cc

@@ -247,7 +247,12 @@ struct c4Indexer : public MapReduceIndexer, c4Internal::InstanceCounted {
         addIndex(&view->_index);
     }
 
+    void finished() {
+        MapReduceIndexer::finished(_lastSequenceIndexed);
+    }
+
     C4Database* _db;
+    sequence _lastSequenceIndexed {0};
 #if C4DB_THREADSAFE
     std::vector<C4View*> _views;
 #endif
@@ -301,6 +306,7 @@ C4DocEnumerator* c4indexer_enumerateDocuments(C4Indexer *indexer, C4Error *outEr
         setEnumFilter(e, [docTypes,indexer](const Document &doc,
                                             C4DocumentFlags flags,
                                             slice docType) {
+            indexer->_lastSequenceIndexed = doc.sequence();
             if ((flags & kExists) && !(flags & kDeleted)
                                   && (!docTypes || docTypes->count(docType) > 0))
                 return true;

CBForest/MapReduceIndex.cc

@@ -357,11 +357,14 @@ namespace cbforest {
             return false;
         }
 
-        void finish(bool success) {
-            if (success)
+        void finish(sequence finalSequence) {
+            if (finalSequence > 0) {
+                index->_lastSequenceIndexed = std::max(index->_lastSequenceIndexed,
+                                                       finalSequence);
                 index->saveState(*_transaction);
-            else
+            } else {
                 _transaction->abort();
+            }
         }
 
     private:
@@ -411,7 +414,7 @@ namespace cbforest {
 
     MapReduceIndexer::~MapReduceIndexer() {
         for (auto writer = _writers.begin(); writer != _writers.end(); ++writer) {
-            (*writer)->finish(_finished);
+            (*writer)->finish(_finishedSequence);
             delete *writer;
         }
     }

CBForest/MapReduceIndex.hh

@@ -97,9 +97,6 @@ namespace cbforest {
         /** If set, indexing will only occur if this index needs to be updated. */
         void triggerOnIndex(MapReduceIndex* index)  {_triggerIndex = index;}
 
-        /** Returns true if indexing completed successfully. */
-        void finished()                             {_finished = true;}
-
         /** Determines at which sequence indexing should start.
             Returns UINT64_MAX if no re-indexing is necessary. */
         sequence startingSequence();
@@ -131,11 +128,15 @@ namespace cbforest {
             key/value pairs. */
         void skipDocInView(slice docID, sequence docSequence, unsigned viewNumber);
 
+        /** Call when all documents have been indexed. Pass the last sequence that was enumerated
+            (usually the database's lastSequence).*/
+        void finished(sequence seq =1)       {_finishedSequence = seq;}
+
     private:
         std::vector<MapReduceIndexWriter*> _writers;
         MapReduceIndex* _triggerIndex {nullptr};
         sequence _latestDbSequence {0};
-        bool _finished {false};
+        sequence _finishedSequence {0};
         bool _allDocTypes {false};
         std::set<slice> _docTypes;